Angora Fire preliminary fire effects
assessment
Ongoing study. Report Version 2: July 19, 2007
Hugh Safford, Regional Ecologist, Pacific SW Region
707-562-8934; hughsafford@fs.fed.us
2
Sampling underway
Sampling completed
4
Fire perimeter
1
2
3
Untreated Area
Jeffrey pine-White firLodgepole pine
No fuels treatment
Treated Area
Jeffrey pine-White fir
Thin & salvage 1996-1998
Precommercial thin (hand) 2003-2004
Activity fuels pile burn 2005
Point-center-quarter transects sampled July 8, 18, 19, 2007
Transect length 220 to 500 m, 10-16 sampling pts each,
random distance intervals (between 15-45 m). Variables
measured: species, dbh, ht, scorch ht, torch ht, bole char ht,
% crown scorch, % crown torch
3
Area of Transect 1: no treatment
Area of Transect 2: treated for fuels 1996-2005
Angora Fire preliminary fire effects assessment, v.2 (7/19/07)
Quantitative comparison of transects, Angora Creek area
25
ca. 370 meters
Meters
20
15
ScorchHt
CharHt
10
5
Untreated
Treated
0
0
1
2
3
4
5
6
7
8
9
10 11
12
13 14
15 16
17
Sampling Point
Transect 3
35
ca. 500 meters
Untreated
30
Treated
20
ScorchHt
CharHt
15
10
5
0
17
Transect 4
16 15
14 13
12
11 10
9
8
7
6
5
4
3
2
1
0
Sampling Point
Changes in scorch height and bole char height along the
linear courses of Transects 3 and 4 (see map for locations),
which sample the transition from untreated to treated forest.
The black vertical line represents the approximate boundary
of the fuels treatment. Error bars represent +/- one standard
error.
Meters
25
4
Angora Fire preliminary fire effects assessment, v.2 (7/19/07)
Quantitative comparison of transects, Angora Creek area
120
ca. 370 meters
Percent of canopy
100
80
% Crown
Scorch
60
% Crown
Torch
40
20
Untreated
Treated
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17
Sampling Point
Transect 3
120
80
% Crown
Scorch
% Crown
Torch
60
40
20
Untreated
Treated
0
17 16 15 14 13 12 11 10
Transect 4
9
8
7
6
5
4
3
2
1
0
Sampling Point
Changes in percent crown scorch (needles browned) and
percent crown torch (needles combusted) along the linear
courses of Transects 3 and 4 (see map for locations). The
black vertical line represents the approximate boundary of the
fuels treatment. All trees in the untreated portion of Transect
4 exhibited 100% crown scorch. Error bars represent +/- one
standard error.
Percent of canopy
100
5
Angora Fire preliminary fire effects assessment, v.2 (7/19/07)
Quantitative comparison of transects, Angora Creek area
1.00
Proportion surviving fire
Untreated
Treated
0.75
0.50
0.25
0.00
1
2
3
4
5
6
7
8
9
10
11
12
13
Sampling Point
14
15
16
Transect 3
1.00
Treated
0.75
0.50
0.25
Proportion surviving fire
Untreated
0.00
16
15
14
Transect 4
13
12
11
10
9
8
7
6
5
4
3
2
1
Sampling Point
Changes in tree survival along the linear courses of Transects
3 and 4 (see map for locations). The black vertical line
represents the approximate boundary of the fuels treatment.
The Y-axis represents the proportion of sampled trees
surviving at each point. No trees survived in the untreated
forest sampled along Transect 4. These mortality estimates
are based on first-order fire effects only and will likely change
as long-term mortality agents (insects, etc.) assert themselves.
6
7
Angora Fire preliminary fire effects assessment, v.2 (7/19/07)
Quantitative comparison of transects, Angora Creek area
200
180
160
140
120
100
80
60
40
20
0
t = 1.202, df = 4,
P = 0.296*
t = 7.624, df = 50,
P < 0.0001*
t = 5.271, df = 30,
P < 0.0001*
Stem density
(trees/acre)
Number of trees
>5” dbh (diameter
at breast height)
per acre
Tree cover (%)
Tree canopy
cover, from
LTBMU
vegetation map1
Untreated
Treated
% mortality
Percent of trees >5” dbh
(diameter at breast
height) killed by fire.
This is a preliminary
estimate based on firstorder fire effects.
* t-test. Error bars represent +/- one standard error.
1 Untreated area cover estimated from polygons mapped immediately adjacent to
treatments
8
Angora Fire preliminary fire effects assessment, v.2 (7/19/07)
Quantitative comparison of transects, Angora Creek area
70
t = 11.942, df = 206, P < 0.0001**
60
50
Z = 10.274, P < 0.0001*
Feet
Z = 10.955, P < 0.0001*
40
Untreated
30
Treated
20
10
0
Crown torch
height
Mean height limit
of torching (needle
combustion) in the
tree canopy1
Crown scorch
height
Bole char height
Mean height limit
of scorching
(needle scorch) in
the tree canopy
Mean height limit of
tree bole (trunk)
charring from surface
fire2. This is an
estimate of surface
flame length.3
*Wilcoxson two-sample (nonparametric) test; ** t-test.
1 81% of trees (87/108) in the untreated samples had torching effects to their crowns;
only 11% (11/100) of trees sampled in the treated area showed torching effects. Mean
torch height of trees in the treated area actually exhibiting torching was 14.4 feet.
2 100% of trees sampled in the untreated area received bole char; 19% of trees
(19/100) in the untreated area showed no bole char whatsoever and 36% showed bole
char <1.5 feet in height.
3 Usually an overestimate due to bark combustion.
9
Angora Fire preliminary fire effects assessment, v.2 (7/19/07)
Quantitative comparison of transects, Angora Creek area
100
90
Z = 9.726, P < 0.0001*
80
Z = 10.338, P < 0.0001*
Percent
70
60
Untreated
50
Treated
40
30
20
10
0
% Crown scorch
Mean percent of
tree crown
scorched by fire
(needles browned)
% Crown torch
Mean percent of tree crown
burned by fire (needles
combusted)1. 41% of trees
(44/108) sampled in the
untreated area had >90%
crown combustion
* Wilcoxson two-sample (nonparametric) test; error bars are +/- one standard error
1 Of the 11 trees in the treated area exhibited crown torching, mean % crown torch was
25.1% (median = 12.5%).
10
Angora Fire preliminary fire effects assessment,
Version 2 (7/19/07)
Summary
Angora fuels treatments 1996-2005:
1. Fuels treatments significantly reduced tree canopy
continuity and surface fuels (surface fuels data
collection underway) in the area adjacent to the Tahoe
Paradise subdivision
2. Fuels treatments significantly decreased tree mortality
• Tree mortality based on first-order estimates was about
77% in untreated areas, about 21% in treated areas
3. Fuels treatments significantly lowered flame lengths and
reduced the effects of fire to the tree canopy
• 100% of trees in the untreated sample had torching
effects to their crown, vs. about 11% in the treated
sample
• The vertical extent of crown torching, crown scorching,
and bole char was much greater in the untreated area
• Surface flame lengths (as estimated by bole char)
averaged more than 32 feet in the untreated area,
compared to about 7.5 feet in the treated area
• Within the untreated sample area, crowns in most trees
were completely scorched, and more than 40% of trees
had >90% of their crowns combusted by fire
4. Fuels treatments in the Angora Creek area significantly
changed fire behavior, reduced fire effects to the
ecosystem, and acted to slow and ameliorate the
intensity of the fire as it approached homes in the Tahoe
Paradise subdivision